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Mean temperature of winding when current falls

  • Thread starter DevonZA
  • Start date
  • #1
181
6

Homework Statement


upload_2016-5-1_12-0-27.png


Homework Equations


R2=R1(1+alpha(t2-t1))

The Attempt at a Solution


R1=250/5=50ohms
R2=250/3.91=63.94ohms

R2=R1(1+alpha15degrees(t2-t1))
63.94=50(1+1/254.5(t2-15))
t2=

Now I found this online but the answers provided still don't match, 84.25 being the closest.

upload_2016-5-1_12-12-12.png


When I manipulate the equation I get a totally different answer:
63.94=50(1+1/254.5(t2-15))
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15
1.274=t2-15
t2=1.274+15=16.274 degrees

Please help me understand where I am going wrong.
 

Answers and Replies

  • #2
cnh1995
Homework Helper
Gold Member
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where I am going wrong.
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15
upload_2016-5-1_12-12-12-png.100061.png

Is this from B.L. Theraja?
 
  • #3
181
6
Not sure I found it online
 
  • #4
cnh1995
Homework Helper
Gold Member
3,301
1,068
Not sure I found it online
It is from B.L. Theraja. The page looks familiar. The red line in the above post is your error.
 
  • #5
181
6
What have I done wrong though? Every way I enter it into my calculator yields an incorrect answer
 
  • #6
cnh1995
Homework Helper
Gold Member
3,301
1,068
63.94/50=(1+1/254.5(t2-15))
1.2788/1+1/254.5=t2-15[/\QUOTE]
This step is wrong. Check the sequence of operations.
 
  • #7
181
6
Ah I got it :-) thank you
 

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